I had the same problem with the pt_BR.po file and I notice that the pt.po also has less entries than the
Spanish one. We have to be attentive because maybe there are other modules out of date too.
I updated the file with this command:
msgmerge -U pt_BR.po pirut.pot

Regards,
Igor Pires Soares

String merging with latest POT files is Maintainer/Translator's choice.

whenever you get "P" status for POT file in module, please merge your 
language file with that
as this is more reliable method.

> We (french translators) are lacking 453 entries from the spanish.
>
> Can you explain that?
>
>   
this is true for all packages

regards